E scherichia coli DNA polymerase III is responsible for the high level of spontaneous mutations in mutT strains

Summary Reactive oxygen species induce oxidative damage in DNA precursors, i.e. dNTPs , leading to point mutations upon incorporation. E scherichia coli mutT strains, deficient in the activity hydrolysing 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine 5′‐triphosphate (8‐oxo‐ dGTP ), display more than a 100‐fold higher spontaneous mutation frequency over the wild‐type strain. 8‐oxo‐ dGTP induces A to C transversions when misincorporated opposite template A . Here, we report that DNA pol III incorporates 8‐oxo‐ dGTP ≈ 20 times more efficiently opposite template A compared with template C . Single, double or triple deletions of pol I , pol II , pol IV or pol V had modest effects on the mutT mutator phenotype. Only the deletion of all four polymerases led to a 70% reduction of the mutator phenotype. While pol III may account for nearly all 8‐oxo‐ dGTP incorporation opposite template A , it only extends ≈ 30% of them, the remaining 70% being extended by the combined action of pol I , pol II , pol IV or pol V . The unique property of pol III , a C ‐family DNA polymerase present only in eubacteria, to preferentially incorporate 8‐oxo‐ dGTP opposite template A during replication might explain the high spontaneous mutation frequency in E . coli mutT compared with the mammalian counterparts lacking the 8‐oxo‐ dGTP hydrolysing activities.